Tapes having pressure-sensitive adhesive layers exceeding 0.1-0.2 mm in thickness tend to be difficult and expensive to manufacture and to have low shear strength. For applications requiring greater thickness, foam-backed pressure-sensitive adhesive tapes such as disclosed in Canadian Pat. No. 747,341 are often employed. However, the porous nature of the foam involves a number of problems such as a tendency to wick liquids. The elastic memory of some foams tends to cause them to lift from low spots on rough or uneven surfaces. Foam layers of less than about 1.0 mm are difficult to manufacture and hence rather expensive.
Brochman U.S. Pat. No. 3,565,247 was in part directed to the problem of economically producing pressure-sensitive adhesive layers exceeding 0.1 mm in thickness, disclosing a microcellular adhesive layer which is both a foam and a pressure-sensitive adhesive. When compressed to half its original thickness, the microcellular adhesive layer typically shows less than 5 percent recovery. Apparently the surfaces at the opposite sides of each cell adhere to each other to inhibit recovery. Such tapes are not on the market.